This invention relates to system or process controllers and more specifically to nonlinear, time-variable predictive controllers in general, and particularly those based on Rate Optimal Control (hereinafter ROC). This will enhance operator control because each plant output will appear to be effectively controlled by an individual setpoint. Moreover, this invention teaches a unified and systematic approach to building robust high-performance control systems that can involve hundreds of control loops exhibiting mutual coupling.
Previously, there have been two approaches to designing control systems. The first approach, called the conventional approach, designs a control system incrementally from the bottom up. Starting with individual loops, each process variable is assigned a closed loop driven by a single input single output (SISO) controller, whose set point represented the desired value of the variable. Due to physical interactions between process variables, these loops are not independent of each other. Failure to account for this mutual coupling degrades overall controller performance, and thus, system performance. To reduce these coupling effects, feedforward links and cascade loops are added on an ad hoc basis after the first design pass. This procedure often needs to be repeated several times to achieve satisfactory system behavior. Moreover, considerable control expertise and in-depth knowledge of the controlled process are required to use this approach.
The second approach to control system design is based on modern control theory which suggests there is, and supplies an exact theoretical solution to the design problem. Using this approach, the plant that the controller is being designed for, can be treated as a multiple input multiple output (MIMO) system which allows all of the characteristics of the process variables to be determined. This "text-book" approach however, has not yet been commercially viable because it does not meet several important engineering criteria. First, for plants with hundreds of process variables, the design algorithms are computationally intractable on current hardware. Secondly a controller based on this approach cannot be developed incrementally, nor does it support modular design or distributed architectures.